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Physics/helium balloons


QUESTION: Why do helium-fillled balloons, like you'd find at aa birthday party, lose their ability to stay up, after  a day and then wind up on the floor after the third or fourth day?

ANSWER: Helium is monatomic, and highly mobile due to its low mass. It's able to diffuse through most materials over time, especially something as complex as rubber. The helium slowly leaks straight out through the balloon.

---------- FOLLOW-UP ----------

QUESTION: I also got a Mylar balloon from the same party, which was May 17. It's still up, tethered by a ribbon. How long can I expect it to stay up?

Far longer. It's less permeable due to its tighter molecular structure, it stops exerting pressure at small deflation....but the size and thickness of the balloon are unknown. A few weeks, if space-edge balloons are a guideline. Probably less, like week-long timescales, due to the thinness of the material.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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